Madeleine Champagne

Dégradation enzymatique de l'acide désoxyribonucléique en sous-unités

Deoxyribonucleic acid from calf thymus (mol. wt. = 6.5·106; s20,w = 20.0 S) or chicken erythrocytes (mol. wt. = 8.0·106; s20,w = 27.5 S) has been degraded with a crude enzymic preparation from chicken erythrocytes. Enzymic activity shows a pH optimum close to 5.5 and is strongly inhibited by Mg ions. No appreciable amounts of dialyzable nucleotides are formed during the enzymic digestion. Digested deoxyribonucleic acid from both sources appears to be formed by particles showing a molecular weight of (5.5 ± 0.5)·105. The light-scattering data are compatible with a solution of monodisperse rods having a molecular weight per unit length M/L = 200 ± 20/A. The sedimentation constant s20, w = 5.8 S and the distribution function of the sedimentation constants is very narrow.

Core particle stability critically depends upon a small number of terminal nucleotides.

An apparently homogeneous population of core particles is in fact composed of three subpopulations which behave differently when exposed to a high concentration of ethidium bromide or to 0.6 M NaCl. These subspecies have been identified by the use of several techniques, viz., electron microscopy, sedimentation velocity and circular dichroism. The electrophoretic analysis of their DNA leads to the conclusion that core particle stability critically depends upon a small number of terminal nucleotides.

The structure of Sipunculus nudus erythrocyte chromatin

Abstract The structure of the Sipunculus erythrocyte chromatin has been characterized by electron microscopy and nuclease digestion (staphylococcal nuclease and pancreatic nuclease). Contrary to previous results [1], we were able to isolate and characterize a histone H2B in sipunculid nuclei. Though the histones H2A and H2B were markedly different from their vertebrate homologues, the subunit structure of the chromatin is the same. But the length of the repeat unit of DNA in the chromatin, is 177 ± 5 bp for the sipunculid erythrocyte nuclei, close to that reported for the chromatin of some lower eukaryotes.

Histones d'érythrocytes de poulets: IV. Etude quantitative des histones au cours de la maturation des érythrocytes

Summary Histones from the erythrocytes of chicken were isolated in two groups: the HRA group of arginine rich histones (F 2 a 1 , F 2 a 2 , F 3 ) and the HRL group of lysine rich histones (F 1 , F v , F 2 b); then electrophoresed quantitatively to estimate the distribution of histone components in the blood of normal and anaemic adulte chicken, and the blood of 5 days old chicken. In the 3 cases the relative values of histone to DNA are very similar and near to 1,1; but the proportions of each group HRA and HRL, are different. The 2 groups are identical in normal adult, but in young chicken the HRL group represents only 40 p. cent of the total histones. The 3 lysine rich histones increase from young to adult chicken, especially F 1 and F v , but histone F 3 decreases. These variations are presumably responsible for progressive chromatine condensation during erythrocyte maturation.

Non-histone chromosomal proteins easily extractible from chick erythrocytes

Those non-histone chromosomal proteins which are easily extractible from chick erythrocytes differ substantially from proteins similarly extracted from other tissues of various species. Although a protein P1 was isolated along with histone H1 by extraction of calf thymus chromatin with HC1O4, the same procedure did not extract this protein from chick erythrocyte chromatin of either normal or regenerating blood. Likewise , non-histone proteins extracted with 0.35 M NaCl from calf thymus differed from those of normal chick erythrocytes, which were qualitatively identical but quantitatively inferior to those of regenerating blood. The major protein of about 25 000 molecular weight, totally extracted with 0.35 M NaCl from calf thymus, was not found in chick erythrocyte chromatin, but rather another major protein of about 35 000 molecular weight was partially extracted from erythrocytes.

Electron microscopic visualization of nucleosomal organization in B12 starved and control Euglena chromatin

Abstract Euglena chromatin, spread according to the Dubochet technique, displays the nucleosomal organization with the typical zig-zag conformation following short periods of digestion with micrococcal nuclease. After comparative kinetic experiments on vitamin B12 starved and control Euglena nuclei, a larger percentage of monosomes appears after 2 mm. in the starved chromatin (86%) compared to the control (59%). No difference is found for longer period of incubation.

Comparison between histones FV and F2a2 of chicken erythrocyte: II. Interaction with homologous DNA

The conformation and stability of artificial complexes between chicken erythrocyte DNA and homologous histones FV and F2a2 was studied by circular dichroism (CD) and thermal denaturation followed by both absorbance and CD measurements. The complexes are made after a stepwise potassium fluoride gradient dialysis without urea and studied at low ionic strength (10-minus 3 M). 1) No structural changes of the DNA can be detected up to r equals 0.2 with FV and r equals 0.6 for F2a2. With FV at higher values of r the CD spectrum is altered, indicating the organization of DNA and histones in some kind of aggregate. 2) The conformation of histone molecules inside the complexes is not related to the ionic strength of the medium but to an effective ionic environment close to 0.1 M. This ionic strength would also correspond to the melting temperature of histone-covered DNA. 3) From the analysis of the absorbance melting profile the length of DNA covered with an histone molecule can be estimated. A good agreement is found between the negative charge of this piece of DNA and the net positive charge of the histone. 4) Since the CD transition at 227 nm occurs before the second absorbance transition at 280 nm, the DNA is stabilized no longer by native histone but partially or fully denatured histones. The helical regions of the histone molecule are not involved in the binding process, which appears to be almost purely coulombian and most likely related to some structural fit between the pattern of negative charges in the DNA helix and that of positive charges along the peptide chain.

Histones d'érythrocytes de poulets: III. Mise en évidence de l'hétérogénéité du fragment N-Terminal de l'histone spécifique

Summary After splitting the molecule of chicken erythrocyte specific histone (Fv) with cyanogen bromide we have isolated three fractions, by chromatography on a carboxy-methyl-cellulose column eluted with an ionic strength gradient, buffered at pH 4,3 : 2 N-terminal fractions A1 and A2 and the C-terminal fraction B. The results of amino-acid analysis and N-terminal determination of the tryptic peptides of the two N-terminal fractions are in complete agreement with the microheterogeneity which has been recently suggested by Greenaway and Murray : at amino-acid no 15, a glutamyl residue in the fraction A1, and an arginyl residue in the fraction A2 have been found.